1. Field of the Invention
This invention relates to a process for the preparation in high yield of a polybutadiene high in 1,2 microstructure and syndiotactic in character. More specifically this process involves the polymerization of 1,3-butadiene in the presence of a novel catalyst composition.
2. Related Prior Art
U.S. Pat. No. 3,778,424 discloses the preparation of 1,2-polybutadiene which is syndiotactic in character and uses for the polymerization of 1,3-butadiene a catalyst composition comprising (a) a soluble cobalt compound, (b) an AIR.sub.3 compound in which R is a hydrocarbon radical of 1-6 carbon atoms, and (c) CS.sub.2. The soluble cobalt compound is defined as including, amoung various other compounds (1) a cobalt salt of an organic carboxylic acid of at least 6 carbon atoms, such as cobalt octoate and cobalt naphthenate and (2) a complex of a cobalt halide, such as CoCl.sub.2, with "a tertiary amine, e.g. pyridine, triethylamine, tributylamine and dimethylaniline, . . . ; and an N,N-dialkylamide, e.g., N,N=dimethyl formanide, N,N-dimethyl acetamide and N,N-diethyl formamide." The only such complex exemplified in the patent is the CoCl.sub.2 complex with pyridine.
In the above patent it is indicated that the prior art method of preparing syndiotactic 1,2-polybutadiene is unsatisfactory because of low yields as well as unsatisfactory physical properties. However, the best yield shown in the patent is in Table 5 where the control experiment shows a yield of 56%. Moreover, the CoCl.sub.2 -pyridine complex used in Example 13 produces a yield of only 38%.
As indicated by the same patentees the melting point of 200.degree.-210.degree. C for the polymers produced by their process makes it difficult to process these polymers. To remedy this problem patentees suggest the use of an organonitrile as a fourth catalyst component to lower the melting point to as low as 100.degree. C. However, as shown in Examples 15-28, the presence of the nitrile also has an adverse effect on the yield (10-35%) and on the 1,2 content, taking it as low as 79%.